Multiturn helical potentiometer



June 22, 1965 M. E. SEKERICH 3,191,137

MULTITURN HELICAL POTENTIOMETER Filed Sept. 18, 1962 2 Sheets-Sheet l INVENTOR. MICHAEL. E. $EKER LCH'.

ATTORNEYS.

June 22, 1965 M. E. SEKERICH MULTITU'RN HELICAL POTENTIOMETER 2 Sheets-Sheet 2 Filed Sept. 18, 1962 G I F INVENTOR.

Ml CHAEL .E S E KERIC H BY Mar/31 m ATTORNEYS.

United States Patent 3,191,137 MULTITURN HELICAL POTENTIOMETER Michael E. Sekerich, 405 E. 94th St., Brooklyn, N.Y. Filed Sept. 18, 1962, Ser. No. 224,460 12 Claims. (Cl. 338-443) along the helix.

In the past the helically wound turns of resistance element was carried on a core which had to have the same coefficient of expansion as the core; otherwise, under an increased temperature, the core would stress the resistance element carried on it and would eventually tear the element.

outer face of the core, and the cutting of that groove was a delicate and expensive operation, especially in ceramic or other fragile non-conductive materials, but ceramics were almost the only available materials of suitable heat coefiicient for supporting the wire helix, despite their tendency to fracture and split off angular fragments that interfered wtih the smooth operation of the sliding contact, so that the helix became worn and uneven in size and resistance.

It has been attempted to overcome some of these and other difficulties by laying the resistance wire loosely in a helical channel and setting the slide contact under the helix wire so as to lift the wire at the front of the contact, but this involved use of a special wire suitable to withstand the bending by the slide and therefore imposed limits on the type of resistance elements which could withstand this rigorous flexing. Most, if not all, prior devices employed a sliding brush which pressed upon a helically wound length of resistance element supported on a convex surface- In order to prevent the brush from shorting more than one turn of element, the helix had to be quite large and a core of appreciable length employed. Furthermore, the brush could not maintain good electrical contact with the helical resistance Wire because these devices employed a simple length of wire, typically of the order of .001 inch in diameter, which. provided a relatively high resistance per unit length.

Other attempts at overcoming prior problems in prior potentiometer designs have included the use of sliders adapted to slide longitudinally back and forth along a slider arm guided by grooves in a core or by a special guide helix other than the resistance wire itself. While being meritorious, such potentiometers have not readily adapted themselves to long resistance wire lengths in miniature or miniaturized infinite resolution potentiometers and have not solved the problems related to the cores.

According to the present invention, the foregoing and other difliculties and objections are overcome and a more rugged, or more economical structure is produced, buildable from a wider range of materials, more resistant to the vicissitudes of long use, and miniaturization.

In the form shown, the core may need no grooves to hold the helix wire, and the wire is wound with slightly spaced turns, and the slide is shown as riding on the upper curved facing surfaces of two adjacent turns of the helix.

Any difficulty in winding the helix with suitably spaced turns is readily avoided by winding suitably insulated wire, preferably with turns lying close against each other and then abrading the exposed face of the insulation to Often, the wire of the helix was laid in a channel in the a expose the upper faces of the turns, as by a suitable sandblast-like abrasive tool. Thus, the turns of wire are relatively fixed close together, covering an extremely narrow band in width and making possible a small device. The resistance element may typically be wound directly around the core or may comprise a plurality of helically wound turns wound about a core of its own, then helically placed on a potentiometer core.

Avoidance of the need for grooves enables any suitable core material to be used to provide a smooth cylindrical surface. The short-circuited turn to the slide contact is constant and may be ignore-d for most practical purposes.

The small gap created by the adjacent turns of resistance winding provide a helical path for the contact to follow and thus generally eliminate the need for additional mechanism to drive the contact in a helical manner, especially in a small potentiometer.

The contact usually embodies the form of a suspended slide wire of a diameter approximately that of the helix wire. This suspended contact wire slides upon the helix created by the resistance element in traversing the band of resistance element.

Other features and advantages will hereinafter appear in the accompanying drawings.

FIG. 1 shows a side view, partly diagrammatic, of the potentiometer.

FIG. 2 shows the end view of FIG. 1.

FIG. 3 shows the slide support and fragmentary perspective.

FIG. 4A shows a fragment of the core and helix winding at line 4-4 of FIG. 2.

FIG. 4B shows a fragment of the core using an alternative abraded insulated winding; from that shown in FIG. 4A.

FIG. 5 shows diagrammatically, in section, a potentiometer on line 5-5 of FIG. 1 with a finely adjustable form of stop including an outer cover.

FIG. 6 shows diagrammatically a detail of the stop fine adjustment.

FIG. 7 shows an alternative form of slide suspension.

FIG. 8 shows diagrammatically the variable circuit contacts in an infinite resolution potentiometer helix windmg.

The device shown includes a smooth, cylindrical, hollow core 10 wound with the desired resistance wire 11 as diagrammatically shown in FIG. 1, with ends terminating at 12 and 13 in the core, which may be ceramic, fused mica, or other high nonconducting materials of high stability with coefiicient of heat expansion close to that of the wire. The helix wire may be of any suitable material for use as a resistance winding; and the coils, closely but distinctly spaced, are diagrammatically shown in FIGS. 4A and 4B.

The desired spacing may be obtained by winding close together the turns of insulated resistance wire, preferably enameled, and then abrading the insulating material, as by sandblast-type methods to expose the top curved surface of the wire and thus obtain a narrow conductive track of exposed wire, permitting hitherto impossible miniaturization of the whole device, particularly in an infinite resolution potentiometer.

Extending through the core 10 so as to turn freely in it is shown a shaft 14 with elongated pinions 15 integral to it mounted in an insulating hub forming part of a circular mounting plate 16. This plate carries end brackets 17 and 18 to serve as end carriers for the sliding contact pick up wire 19.

The shaft 14 is shown as carried in an aluminum lid 26 a pair of conventional ball bearing races 28, 29 to enable the brackets 17 and 18 to serve as firm foundations for guiding the contact wire 19. For the potentiometer during operation a'cap 3t? resting on the cover 26 encloses the mechanism, is usually provided as shown in FIG. 5.

In the present embodiment shown, the brackets 17 and 13 may have a limited resilience, to enable them to yield slightly as the contact wire 19 travels up or down the helix, and to further yield to that end, they each carry an end of the contact wire 19 by tabs 20 pivoted loosely at a point 21 on its bracket arm 17 or 13.

The tabs 2% are usually upstanding before assembly. The contact wire 19 is attached to one tab Zil and spanned over to reach the other tab 20 so that both tabs are sprung. The tension of the sprung tabs 20 urges pressure of the suspended contact Wire 19 on the helixturns 11, arced over the helix 11, and thus prevents the suspended wire 19 from jumping to an adjacent valley under shock and vibration.

As shown in FIGS. 1 and 2, the contact wire 1d spans the face of the core 10, so as to lie in the valley between two adjacent turns of the helix, and to rest wholly on the two facing curved wire surfaces as shown in FIG. 4. The contact wire 19 is preferably a round, hard metal wire to resist wear, and to overcome its high electrical resistance it is usually gold plated from each tab 2% to points 23 where it lies on the helix Wire 11.

The core 10, on its underface, carries a metal conductor ring 25 against which, bare resilient brushes 24, one from each bracket 17, 18 and the ring 25 is connected electrically to the outside terminal 32 by a conductor 31.

The cover 26 of the potentiometer carries a hub 27 by which it may be mounted into a panel.

As stated above, the contact wire 1h, by riding in the valley formed by two adjacent turns of the helix, may run off the valley end of the helix, especially where a potentiometer is provided without a stop mechanism, but automatically runs back into the valley when the shaft rotation is reversed back assisted by the tension of the suspended contact wire 19 exerted by the sprung tabs 20, centrally located in relation to the helix Winding.

Sometimes an end stop is demanded, and the core 10 shown provides space for a finely adjustable stop within a depending circular peripheral wall 40.

To operate the stop device, the shaft 14- as shown in FIGS. and 6 carries elongated pinions 15, meshing with a traveling spur gear 35, which internally is threaded at its center to travel on a threaded shaft 33, held in the fiat top 41 of the lid 26. When the shaft 14 turns in one direction, in the form shown, it turns the internally threaded gear 35 shown as as fast, causing the gear 36 to travel down until a pin 36 from the gear strikes the fixed pin 37 and stops the turning of the shaft 14. When the shaft is reversed, the internally threaded gear turns in the opposite direction until the pin 36 strikes the upper fixed pin 34 and arrests the turning of the shaft 14. Thus the shaft may be stopped at any predetermined point by the setting of the fixed pins.

The bottom view of the alternative hub 16 construction in FIG. 7 shows integral bracket arms 4-2, replacing the brackets 17 and 18, and stamped from a piece of metal forming an angle plate 38. The arms 42 form an angle 39 with the end of shift 1 which is in effect a segment of a circle with the contact wire 19 substantially forming a flexable chord across said segment.

This plate carries its arms 42. at approximately a 120 angle 39, which is satisfactory. Other angles of contact have also proven satisfactory. Either form of device is adapted to an infinitely variable change of adjustment of resistance and is adapted to satisfactorily cover a band of from one to 100 turns of wire in the embodiment as shown in the drawings, by reason of the resilient mount rng.

In FIG. 8 an electrical schematic is shown of the helix resistance wire 11 in infinite resolution winding showing the shorting of two turns of the potentiomter caused by the sliding of the contact wire 19 in the groove formed by the turns.

While the embodiment shown provides for traveling of the contact wire 19 suspended on the arms 17, 18 or on the bracket plate 38, flexing on tabs 20 and pivoted at points 21 on the bracket arms 17, 18, longer helixes may be traversed by the contact wire 19 by providing in conjunction With the present disclosure or separately known means for causing the bracket arms 17, 18 and/ or bracket plate 38 themselves to be moved longitudinally to cover a helix longer than the distance tabs 28 and the pivots 21, might adapt to flex.

In the embodiment shown the very narrow area of winding, whether by space Winding or by abraded insulation providing a maximum area for resistance in a minimum amount of space particularly for an infinite resolution potentiometer and is most adequately adapted to the urgent requirements of present day miniaturization with accurate function.

In miniaturization applications, contact wire and helix wire diameters ranging from .0005 to .004 inch in diameter cover the gamut of most required resistances. Sizes below .0005 lose effectiveness as resistive tracks for the contact wire and have less desirable wear characteristics. Sizes above .004 are also adaptable to other means of pick off.

Having thus described certain embodiments of the invention, what is claimed is:

1. An adjustable resistor, including a helix of spaced wire turns; a cylindrical core on which said helix is wound with exposed curved conductor facing surfaces, a contact wire lying on a substantial are along said helixs curved surfaces in electrical contact therewith spanning said helix, electrical conductor arm holding said contact wire against said substantial are of said helix, and means adapted to cause said contact wire to track along the turns of said helix.

2. An adjustable resistor, including a helix of spaced wire turns; a nonconductive cylindrical core having a coefiicient of expansion about equivalent to that of the said helix wire; said helix wound on said core with exposed curved conductor facing surfaces, a contact wire lying on a substantial are along said helixs curved surfaces in electrical contact therewith spanning said helix, electrical conductor arms holding said contact wire against said sub: stantial arc of said helix, and means adapted to cause said contact wire to track along the turns of said helix.

3. An adjustable resistor, including a helix of spaced wire turns; a cylindrical core on which said helix is wound; said wire turns embedded in electrical insulation with exposed curved conductor facing surfaces, at contact wire lying on a substantial are along said helixs curved surfaces in electrical contact therewith spanning said helix, electrical conductor arms holding said contact wire against said substantial arc of said helix and means adapted to with exposed curved conductor facing surfaces, a rotatable shaft, arms on said shaft, a contact wire lying on a substantial are along said helixs curved surfaces in electrical contact therewith spanning said helix and held by said arms, and means on said arms adapted to cause said contact wire to track along the turns of said helix.

5. An adjustable resistor, including a helix of spaced wire turns; a cylindrical core on which said helix is wound with exposed curved conductor facing surfaces, a rotatable shaft, arms on said shaft, pivotable connections on said arms, and a contact wire lying on a substantial are along said helixs curved surfaces in electrical contact therewith spanning said helix and held by said pivotable connections on said arms said contact wire riding in a track formed by two adjacent turns of said helix. 7

6. An. adjustable resistor, including a helix of spaced wire turns; a cylindrical core on which said helix is wound with exposed curved conductor facing surfaces, a rotatable 5 shaft, arms on said shaft, a contact wire lying on a substantial are along said helixs curved surfaces in electrical contact therewith spanning said helix and held by said arms, and means adapted to move said contact wire on said curved surfaces along the entire width of said helix.

7. An adjustable resistor, including a helix of spaced wire turns; a cylindrical core on which said helix is Wound with exposed curved conductor facing surfaces, a rotatable shaft, an upstanding portion including a pair of arms on said shaft, and a contact wire lying on a substantial are along said helixs curved surfaces in electrical contact therewith spanning said helix resiliently held by said arms, said contact wire riding in a track formed by two adjacent turns of said helix.

8. A finely adjustable resistor, including a helix of spaced Wire turns; an inert hollow cylindrical core having coeificient of expansion matching said wire helix; said helix wound on said core with exposed curved conductor facing surfaces, a rotatable shaft, two arms on said shaft, a flexible tab on each said arm, a contact wire lying on a substantial are along said helixs curved surfaces in electrical contact therewith spanning said helix and held under tension on said arms by said tabs said contact wire riding in a track formed by two adjacent turns of said helix.

9. The device of claim 8 including said flexible tabs adapted to flex longitudinally with relation to the width of said helix as said shaft is rotated.

11). The device of claim 8 including means adapted to move said contact wire and arms longitudinally along the entire width of said helix as said shaft is rotated.

11. The device of claim 8 wherein the contact wire, and the helix wire are of a diameter in the approximate range from .0005 of an inch to .004 of an inch.

12. An adjustable resistor, including a helix of spaced insulated wire turns; a cylindrical core in which said helix is wound; a plurality of said wire turns and having said insulation of said turns in contact and with exposed uninsulated curved conductor facing surfaces, a contact wire lying on a substantial are along said helixs curved surface in electrical contact therewith spanning said helix, electrical conductor arms holding said contact wire against said substantial arc of said helix, and means adapted to cause said contact wire to ride in a track formed by two adjacent turns of said helix.

References Cited by the Examiner UNITED STATES PATENTS 1,535,898 4/25 Camp 338-148 1,561,137 11/25 Burns 338-143 1,880,239 10/32 Crouse 29155.68 2,927,367 3/60 Jarvis 29--155.68 3,069,646 12/ 62 Harison et al 338-443 FOREIGN PATENTS 3 84,731 12/32 Great Britain. 762,1 12 11/56 Great Britain.

RICHARD M. WQOD, Primary Examiner.

ANTHONY BARTIS, Examiner. 

3. AN ADJUSTABLE RESISTOR, INCLUDING A HELIX OF SPACED WIRE TURNS; A CYLINDRICAL CORE ON WHICH SAID HELIX IS WOUND; SAID WIRE TURNS EMBEDDED IN ELECTRICAL INSULATION WITH EXPOSED CURVED CONDUCTOR FACING SURFACES, CONTACT WIRE LYING ON A SUBSTANTIAL ARC ALONG SAID HELIX''S CURVED SURFACES IN ELECTRICAL CONTACT THEREWITH SPANNING SAID HELIX, ELECTRICAL CONDUCTOR ARMS HOLDING SAID CONTACT WIRE AGAINST SAID SUBSTANTIAL ARC OF SAID HELIX AND MEANS ADAPTED TO CAUSE SAID CONTACT WIRE TO TRACK ALONG THE TURNS OF SAID HELIX. 